Specifically, the endless track structure of the present invention is of the type wherein a suspension support beam is provided with idler wheels at opposed ends thereof with one of the wheels being adjustable to tension an endless track. A drive sprocket is connected to the support beam and adapted to connect to the drive axle of a vehicle whereby to impart rotation to the endless track supported about the idler wheels and the drive sprocket. Generally, this type of endless track structure is known in the art as disclosed, for example, by U.S. Pat. Nos. 6,318,484, 6,006,847 and 5,388,656. However, known prior art structures do not provide the flexibility, shock-damping features and adjustability that is required when such endless track structures are used on all-terrain vehicles where the vehicle is displaced at high speed over hard, rough terrain or snow. They also require many parts in their assembly and this leads to frequent break-downs and repairs. Some of these structures also use leaf-spring structures for shock absorption, therefore contributing to a heavy suspension assembly.